This invention is related to the field of digital video signal processing, and more particularly to processing a digital high definitition television signal by a digital video tape recording/reproducing system.
Digital high definition television (HDTV) systems have recently been proposed. One such system, proposed by the Advanced Television Research Consortium and generally known as the AD-HDTV system, prioritizes and digitally processes a high definition television signal subjected to MPEG-like variable length coding. MPEG is a standardized coding format being established by the International Organization for Standardization. The standard is described in the document xe2x80x9cInternation Organization for Standardization,xe2x80x9d ISO/IEC DIS 11172, CD 11172-1, CD 11172-2, CD 11172-3 Rev. 1, version of Jan. 21, 1992, Coding for Motion Pictures and Associated Audio for Digital Storage Media, which document is incorporated herein by reference for description of the general code format. Aspects of the AD-HDTV system are described in U.S. Pat. No. 5,168,356-Acampora et al. In the system described by Acampora, codewords are prioritized to reflect high priority and relatively lower priority standard priority information in a digital datastream. Codewords are formed into transport packets, or cells. Each transport packet includes a packed data payload section prefaced by a header which contains information identifying the associated payload data.
It is desirable to record and reproduce (playback) such a digital HDTV signal by means of a device such as a consumer video cassette recorder (VCR) for example. Such a device uses two or more magnetic heads mounted on the periphery of a rotating drum. The heads are physically separated by a predetermined amount, and record/reproduce a signal in alternate successive angled tracks on a magnetic tape. Both consumer and professional VCRs often include provision for special xe2x80x9ctrickxe2x80x9d features such as variable speed forward (eg., fast search), reverse and freeze-frame. The disclosed recording/reproducing apparatus is capable of reproducing pre-recorded media, and can record both a received broadcast high definition television such as a signal in accordance with the AD-HDTV format, as well as live pictures from a camera. The present invention is directed to means for facilitating the operation of high definition digital video recorder/reproducing apparatus, with respect to special features operation in particular.
In accordance with the principles of the present invention, digital video tape recording/reproducing apparatus suitable for processing a high definition television signal includes provision for controlling the occurrence of high priority image information. Such information is selectively recorded at normal speed at predetermined regions on tape tracks so as to be appear along a tape head scanning path associated with specific reproducing speeds greater than normal (eg., 20xc3x97 normal). Input high priority data may be reordered or duplicated for recording in predetermined tape regions. In either case, input data is manipulated to produce a viewable image during reproduction at higher than nominal reproduction speeds, eg., in a fast search mode. In an illustrated system for receiving an MPEG coded datastream, an output datastream at greater than normal reproduction speed comprises either intracoded I-frame data cells only, or a whole Groun of Pictures (GOP).
In accordance with a feature of the disclosed system, feature bits/indicators containing operating instructions for subsequent receiver circuits are added to the datastream.
In accordance with another feature of the disclosed system, information is processed at the MPEG codeword level. An input MPEG coded datastream is decoded to MPEG words, then selected MPEG words are re-coded and recorded in tape packets.